1. Field of the Invention
The present invention relates to a vehicular air conditioning unit for use in automobiles, and more particularly to a vehicular air conditioning unit having a guiding structure, for guiding liquid droplets produced in the vicinity of an expansion valve due to moisture condensation.
2. Description of the Related Art
Automobiles have a passenger compartment for accommodating passengers on board. When a passenger in the passenger compartment feels hot, the passenger may control a cooling mechanism mounted in the automobile, in order to adjust the temperature inside the passenger compartment.
The cooling mechanism includes a compressor, a condenser, a receiver, an expansion valve, and an evaporator, which are connected by piping. A refrigerant circulates through the pipes between the components of the cooling mechanism. Specifically, the refrigerant is compressed by the compressor and then condensed into a liquid form by the condenser. The liquid refrigerant flows through the receiver into the expansion valve. When the liquid refrigerant is ejected from the expansion valve, the refrigerant is quickly expanded into a mist, which is delivered to the evaporator.
The evaporator is supplied with air from the passenger compartment. The refrigerant that flows inside the evaporator deprives the air of heat of evaporation, thus lowering the temperature of the air. At the same time, the refrigerant is evaporated in the evaporator. The evaporated refrigerant then returns to the compressor, which again compresses the refrigerant. The above cycle of operation is repeated in order to continuously cool the passenger compartment.
When the refrigerant mist is ejected from the expansion valve into the evaporator, the refrigerant undergoes adiabatic expansion, thereby lowering the temperature of the expansion valve in the vicinity of the ejection port, as well as the temperature of the pipe that is connected to the ejection port. If the temperature drops significantly, to the dew point or lower, then dew condensation occurs on outer surfaces of the expansion valve and the pipe. If liquid droplets produced by such dew condensation enter into the passenger compartment, then passengers in the passenger compartment may become wet. Entry of excessive liquid droplets into the passenger compartment may possibly cause some of the liquid droplets to reach a CPU, which is positioned near the feet of the passenger in the passenger compartment. Since the CPU could be adversely affected by such liquid droplets, it is necessary to minimize entry of liquid droplets from the cooling mechanism into the passenger compartment.
One widely practiced approach is to wind an insulator, made of an ethylene propylene copolymer or the like, around the expansion valve and nearby piping, thereby suppressing the formation of dew condensation thereon (for details, see Japanese Laid-Open Patent Publication No. 9-303905, for example).
However, in practice, it has proven difficult to sufficiently reduce dew condensation simply by winding an insulator around the expansion valve and nearby piping. Stated otherwise, it is not easy to install an insulator to the extent necessary for reducing dew condensation, unless a skilled worker is called in to do the job. In addition, the process of winding the insulator is complex and takes a long time to complete. Further, since an insulator is needed in the first place, the number of parts used is relatively large, thus increasing the cost of the cooling mechanism.
Japanese Laid-Open Patent Publication No. 2004-98755 discloses a vehicular air conditioning unit, including an expansion valve housed in an expansion valve chamber having a water removal hole for discharging liquid droplets. It is described in this publication that, even when dew condensation occurs in the expansion valve and nearby piping, formed liquid droplets are smoothly discharged from the expansion valve chamber and out of the casing of the vehicular air conditioning unit.